The invention provides a method for simultaneously extracting and purifying phospholipid fatty acid PLFA and deoxyribonucleic acid DNA from the same composting sample, and the extracting method is based on an extraction method of lipid, after phase separation, the lipid enters an organic phase while the DNA is left in a water phase and a solid phase to realize the simultaneous extraction of the PLFA and the DNA finally; the extracting method of the invention has the advantages of simplifying the procedures for extracting the lipid of the composting sample and the DNA, ensuring the identity ofthe information source of the sample, well reducing the error caused by composting sampling to the measuring method, and being more meaningful when the quantity of the samples is small.